A last-ditch remedy for an ailing planet, or a reckless scheme that could be a greater threat to life on Earth than the problem it aims to solve? Opinions are sharply divided on geoengineering--potential massive interventions in the global climate system, intended to forestall the worst effects of climate change.

Last week, participants in the internationalConvention on Biological Diversity(CBD) made their views clear at a meeting in Nagoya, Japan. They included in their agreement to protect biodiversity a moratorium on geo-engineering "until there is an adequate scientific basis on which to justify such activities and appropriate consideration of the associated risks." The moratorium, expected to be in force by 2012, isn't legally binding, and given the preliminary nature of studies in the area it is unlikely to affect researchers in the near future. But some scientists fear that the CBD's stance will sow confusion and delay at a time when governments and research groups are exploring how geo-engineering might feasibly be undertaken if global warming accelerates disastrously.

The CBD agreement coincides with the release of a pair of reports on geoengineering, including a U.S. congressional analysis, published on October 29, that calls for research across the federal government. In his foreword to the report, Bart Gordon (D-Tenn.), the outgoing chairman of the House Committee on Science and Technology, highlights the dangers of stifling research and calls for a "rigorous and exhaustive examination" of geo¬engineering strategies.

"If climate change is one of the greatest long-term threats to biological diversity and human welfare," says Gordon, "then failing to understand all of our options is also a threat." His report singles out the U.S. National Nano¬technology Initiative--a program that incorporates research at 13 federal agencies--as a possible model for coordinating research.

The Nagoya agreement grants an exception for smaller studies conducted in a "controlled setting", but only if they are thoroughly assessed and "justified by the need to gather specific scientific data." Ken Caldeira, a geochemist who studies geoengineering at the Carnegie Institution for Science in Stanford, Calif., finds the agreement's language vague and confusing. "What does 'specific' mean? Who is to determine the necessity of the data? How do I demonstrate a need to do anything?" he asks. Caldeira is also concerned that the agreement does not distinguish between controversial geoengineering technologies intended to block out the sun and less problematic techniques, such as removing carbon dioxide from the atmosphere.

The CBD set a precedent for such language in 2008, when it called for a halt to ocean fertilization activities but allowed small-scale research projects to continue. That ban caused the German government to suspend an ocean fertilization experiment, dubbed LOHAFEX, in the Southern Ocean in early 2009, although the project eventually went forward. Pat Mooney, executive director of ETC Group, an environmental activist organization based in Ottawa, Canada, that lobbied for the geo¬engineering ban, says the issue was advanced by representatives from all parts of the globe, including Norway, Switzerland, Bolivia and the Philippines. "It won't stop small experiments, but governments will think twice before they allow anything on a larger scale," Mooney says.

David Keith, a geoengineering researcher at the University of Calgary in Canada, says he agrees with the basic message that small-scale research should move forward, but large-scale technology deployment should be put on hold. Keith commissioned a separate report, also released on October 29, that explores in detail the costs of injecting sulfur into the upper atmosphere to deflect sunlight. The report suggests that a small fleet of specially designed aircraft could inject 1 million tonnes of sulfur into the stratosphere for just $1 billion-$2 billion a year. That would offset more than half of the global warming so far caused by anthropogenic greenhouse gases, and could be scaled up. "It is certainly the first time anybody has got serious about this," says Keith, who paid for the study through a fund that he manages with Caldeira, and that is provided by Microsoft founder Bill Gates. Keith stresses that the goal is to get a grasp of what a geoengineering program might actually look like, so that scientists can properly focus their investigations into impacts and consequences.

The Intergovernmental Panel on Climate Change (IPCC) is encouraging scientists to expand their geoengineering work, and is planning a meeting in June next year to discuss the scientific basis for geoengineering, its costs, impacts and side effects, and how to treat the issue in the next IPCC assessment. Ottmar Edenhofer, chief economist of the Potsdam Institute for Climate Impact Research in Germany and co-chairman of the IPCC's working group on climate-change mitigation, says that commitments to reducing greenhouse-gas emissions will probably not be enough to meet widely discussed climate goals, such as limiting global warming to 1.5-2 degrees Celsius over the next century.

"Geoengineering is one option, and it should be included in a portfolio of other options," says Edenhofer.

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